The present invention relates to a process for producing a tubular structural element, and to a tubular structural element which is particularly, but not exclusively, suitable for use in the construction of vehicles.
In the construction of vehicles, tubular structural elements are widely used which are of complex shape and cross-sectional dimensions vary widely along their length. Examples of such elements in an automobile are the A-pillar, the B-pillar, or the instrumentation panel beam.
These elements are usually formed into final shape from a tube which prior to the forming process is of constant cross-section. The forming process is carried out in a die and utilises cold or warm fluid pressure forming. Forming tubes into desired shapes using a fluid medium which is supplied internally of the tube under pressure is known. The medium may be small solid balls which collectively act as a fluid, or may be a liquid such as a suitable oil or may be a gas such as air or steam. In this specification the, forming process performed within a die and which utilises a pressurised fluid medium is referred to as a hydro-forming process. The hydro-forming process may be performed using a warm or cold die and/or tube. The hydro-forming process is restricted by the hydro-forming-elongation ratio of the material from which the tube is made and so with a single tube it is only possible for the maximum and minimum cross-sectional dimensions of the final shape of the element to differ by twice the hydro-forming-elongation ratio of the material.
In the present specification the term xe2x80x98hydro-forming-elongation ratioxe2x80x99 of a material is the amount by which the material can be elongated under the conditions of hydro-forming processes.
It is a general aim of the present invention to provide a process for forming, preferably using cold or warm hydro-forming techniques, a tubular structural element having maximum and minimum cross-sectional dimensions which can differ by more than twice the hydro-forming-elongation ratio of the material from which the element is made.
According to one aspect of the present invention there is provided a process for forming an elongate structural element of desired shape being of large and small cross-sectional dimensions at spaced locations along its length, the process including the steps of:
(i) selecting a first tube for forming a first selected length of the element having cross-sectional dimensions within a first range of relatively small cross-sectional dimensions within the hydro-forming-elongation ratio capabilities of the material from which the first tube is formed, said first tube being of constant wall thickness and of a first constant cross-sectional dimension along its length,
(ii) selecting a second tube for forming a second selected length of the element adjacent to the first length, the second length of the element having cross-sectional dimensions within a second range of relatively large cross-sectional dimensions within the hydro-forming-elongation ratio capabilities of the material from which the second tube is formed, said second tube being of constant wall thickness and being of a second constant cross-sectional dimension along its length which is different to said first constant cross-sectional dimension,
(iii) joining adjacent ends of said first and second tubes together, and
(iv) performing forming operations on the first and second tubes to produce the desired shape of the element.
If desired, step (iv) may be performed before step (iii).
Preferably said first and second constant cross-sectional dimensions respectively lie outside said second and first ranges of cross-sectional dimensions, and joining of said first and second tubes includes the steps of:
(v) enlarging one end of the first tube to form a first connection formation of greater cross-sectional dimension than said first constant cross-sectional dimension, and/or
(vi) reducing one end of the second tube to form a second connection formation of lesser cross-sectional dimension than said second constant cross-sectional dimension,
(vii) joining the first and second connection formations together to join said first and second tubes together.
Step (v) and/or step (vi) may be performed using any conventional cold or hot deforming technique, including swaging, drawing or hot or cold hydro-forming.
The first and second connection formations may be fixedly joined together by bonding techniques such as welding.
Alternatively or in addition, the first and second connecting formations may be formed so as to have overlapping marginal end portions which are fixedly secured together by a forming operation which causes the overlapping marginal end portions to be pressed together. Preferably relative axial movement between the marginal portions of the first and second connection portions is controlled as the respective marginal portions are pressed together. In this respect, the overlapping marginal-portions may be adapted by shaping so as to provide a mechanical lock therebetween resisting relative axial movement between the overlapping marginal portions.
Alternatively, or in addition, friction material may be located between the overlapping marginal portions in order to restrain relative axial movement therebetween.
It will be appreciated that the material of the first tube may be the same or different to the material of the second tube and may be of the same or different wall thickness.
The tubes may be symmetrical or asymmetrical in cross-sectional shape.
In accordance with another aspect of the present invention there is provided a process for forming an elongate structural element of desired shape being of large and small cross-sectional dimensions at spaced locations along its length, the process including the steps of:
(i) selecting a first tube for forming a first selected length of the element having cross-sectional dimensions within a first range of relatively small cross-sectional dimensions within the hydro-forming-elongation ratio capabilities of the material from which the first tube is formed, said first tube being of constant wall thickness and being of a first constant cross-sectional dimension along its length,
(ii) selecting a second tube for forming a second selected length of the element adjacent to the first length, the second length of the element having cross-sectional dimensions within a second range of relatively large cross-sectional dimensions within the hydro-forming-elongation ratio capabilities of the material from which the second tube is formed, said second tube being of constant wall thickness and being of a second constant cross-sectional dimension along its length which is different to said first constant cross-sectional dimension,
(iii) selecting an intermediate connection tube having a first end of relatively small cross-sectional dimension and a second end of relatively large cross-sectional dimension;
(iv) joining said first and second tubes together by connecting one end of the first tube to the first end of the connection tube and by connecting one end of the second tube to the second end of the connection tube, and
(v) performing forming operations on the first, second and connection tubes to produce the desired shape of the element.
Preferably the connection tube is connected to the first and second tubes by welding.
Preferably the connection tube progressively increases in cross-sectional dimensions from its first end to its second end at a substantially constant rate along its length. In a preferred embodiment, the connection tube is in the form of a truncated cone.
Various aspects of the present invention are hereinafter described, with reference to the accompanying drawings in which:
FIG. 1 is a schematic illustration of a longitudinal portion of a finished tubular structural element according to the present invention;
FIG. 2 is a more detailed schematic illustration of the element shown in FIG. 1 in the region of jointing between adjacent tubes;
FIG. 3 is a schematic illustration showing first and second tubes for forming respective first and second lengths of the element in FIG. 1;
FIGS. 4, 5 and 6 schematically illustrate alternative configurations for joining the first and second connection formations,
FIG. 7 is an illustration similar to FIG. 1 showing a different embodiment,
FIG. 8 is an illustration showing tubes prior to formation into the tubular element shown in FIG. 7.